The present invention relates to an image forming apparatus such as an electrophotographic copier and laser printer, and more particularly relates to an image forming apparatus having a detachable process cartridge to which an image forming section including a photoreceptor, charging unit and developing unit, and a toner supply section are integrally assembled.
In general, an image forming apparatus such as an electrophotographic copier and laser printer is constructed as follows:
A photoreceptor drum is rotatably provided approximately at a center of the apparatus. Around the photoreceptor drum, there are successively provided a charging unit, exposing unit, developing unit, transfer unit, separation unit, cleaning unit, and discharging unit. In the above components, the photoreceptor drum, charging unit, developing unit and cleaning unit include parts of consumption, the lives of which are limited. Therefore, in order to maintain the quality of copied images, it is necessary to successively replace the parts with new ones . For this reason, a process cartridge is employed, in which the photoreceptor drum, charging unit, developing unit and cleaning unit are integrally accommodated in one casing. In the cases of inspection, repair and maintenance, the process cartridge is withdrawn from the apparatus body for the purpose of cleaning the photoreceptor, replacing the developer, cleaning the charging unit and replacing the cleaning member. After a predetermined number of images have been formed, the process cartridge is replaced with a new one.
To the developing unit described above, toner is supplied by a toner supply unit, which is disposed at a position close to the developing unit, that is, the toner supply unit is disposed at an upper position on the front side of the apparatus. In the case of an image forming apparatus in which images are formed at a middle or high speed, a relatively large amount of toner is accommodated in this toner supply unit. Therefore, a casing of the toner supply unit is constructed to be large and disposed on the front side of the charging unit in such a manner that the toner supply unit occupies the front side of the charging unit provided in an upper portion of the photoreceptor drum.
Toner powder, paper dust and solid oxide film tend to adhere to a discharging wire electrode which is provided in the charging unit. When the above adhering materials are accumulated on the electrode, electrical charges are not uniformly distributed, in other words, the intensity of the distributed electrical charge becomes uneven. Therefore, density of a copied image becomes uneven. For this reason, it is necessary to clean the wire discharging electrode at an appropriate time, and a discharging wire cleaning means is provided to fulfill this requirement.
Discharging wire cleaning means provided in the conventional charging unit will be described as follows.
(1) The process cartridge is completely detached from the image forming apparatus, and the cleaning member is manually operated so that the wire electrode can be cleaned.
(2) A toner supply unit disposed on the front side of the process cartridge is moved in a transverse or downward direction so that the front side of the charging unit can be opened, and then a handle of the cleaning member is held by an operator and the cleaning member is manually pulled out. Then the wire electrode is cleaned.
(3) According to Japanese Utility Model Publication Open to Public Inspection No. 168451/1988 applied by the present applicant, the toner supply unit is disposed at a position except for the front side of the charging unit. An operation handle of the discharging wire cleaning means penetrates a casing the image forming apparatus, so that the discharging wire can be cleaned by operating the handle from the outside of the apparatus.
In the case of item (1), it is necessary for an operator to take out the process cartridge from the image forming apparatus each time the discharging wire of the charging unit is cleaned. Accordingly, the operation property is remarkably lowered.
In the case of item (2), the structure to withdraw the toner supply unit is complicated, and further the operation property is not good.
In the case of item (3), the discharging wire cleaning member penetrates the casing. This structure is limited to a case in which the toner supply unit does not exist on the front side of the charging unit.
As disclosed in Japanese Patent Publication Open to Public Inspection No. 2433/1976, the photoreceptor drum, charging unit, developing unit, toner bottle and cleaner, which are components necessary for image formation, are integrated into one unit in a process cartridge, and each unit is positioned in the process cartridge in such a manner that each unit is fixed to a frame of the cartridge. In the above structure, the dimensions of the frame are increased, so that it is difficult to maintain the accuracy and rigidity of the parts, and in the case where a plurality of parts are used to compose the frame, the number of parts is increased, which raises the costs of the apparatus.
In an image forming apparatus to which a clam-shell type structure is adopted, it is common that a lock lever is operated when an upper body is opened, and a portion of the upper body is pressed by an operator when the upper body is closed. In the case disclosed in Japanese Utility Model Publication Open to Public Inspection No. 130448/1985, a handle exclusively used for opening and closing is provided. It is obvious that the operating property can be improved in the opening and closing operation of the upper body when the handle is provided. However, when the upper body is opened, it is necessary to release the lock. Therefore, the handle is indispensable. However, when the handle is used for closing the upper body, the handle is operated in an opposite direction, so that the structure becomes complicated. Further, when an exclusive handle is provided, the number of parts is increased, which raises the manufacturing cost.